Process for the production of alumina from the mineral component of solid fuels

Abstract

The invention relates to a process for the production of alumina from mineral component of solid fuels containing aluminum, silicon and iron oxides. The process comprises burning a mixture of a solid fuel with limestone in the following molar ratios of limestone to said oxides: CaO:SiO 2 =2.0, CaO:Al 2 O 3 =1.3-1.8, CaO:Fe 2 O 3 =1.0, at 1700°-1900° C. As a result, a melt is obtained containing calcium compounds: 2CaO.SiO 2 , 12CaO.7Al 2 O 3 , CaO.Al 2 O 3 , CaO.Fe 2 O 3 . The melt is cooled and leached with soda solutions for extracting alumina. The sludge remaining after the leaching is suitable for Portland cement production. The invention enables a considerable enlargement of the range of starting products for aluminum and cement industries due to the use of the mineral component of solid fuels, an about twofold reduction of capital investments in the alumina production and reduction of the fuel consumption by 30-40%.

What is claimed is: 
     
       1. A process for the production of alumina directly from solid fuels containing aluminum, silicon and iron oxides during the burning of said fuels, comprising mixing the solid fuel with limestone with the following molar ratios of limestone and said oxides: CaO:SiO 2  = 2.0, CaO:Al 2  O 3  = 1.3-1.8, CaO:Fe 2  O 3  = 1.0; burning the resultant mixture at about 1700°-1900° C to obtain a product containing calcium compounds 2CaO.SiO 2 , 12CaO.7Al 2  O 3 , CaO.Al 2  O 3 , CaO.Fe 2  O 3  in the form of a melt; cooling the resultant melt to 1300° C at a rate of about 6° C per minute, and from 1300° C to ambient temperature to convert dicalcium silicate contained in the product from the beta-modification to the gamma-modification and leaching the cooled product with a soda solution to extract alumina, leaving a sludge consisting essentially of dicalcium silicates. 
     
     
       2. The process of claim 1, wherein 7 to 20 weight % of the total limestone is added to the solid fuel prior to burning, and the remaining 80 to 93 weight % is added to the melt. 
     
     
       3. The process of claim 1, wherein the cooling from 1300° C to ambient temperature is conducted at a rate of about 10° to 12° C per minute.